Methods of and apparatus for assembling articles

ABSTRACT

Groups of elongated paramagnetic articles, having headed ends, are aligned with and moved through groups of bores in an assembly fixture after which washers are placed over the ends of the elongated articles. The assembly fixture is inverted and the washers slide along the articles into engagement with the headed ends of the articles and are held thereagainst when the fixture is returned to an original position. The lower unheaded ends of the articles are positioned in holes formed in a wafer after which the elongated articles are released to drop slideably in the holes in the wafers until the washers engage the top surface of the wafer.

United States Patent Appl. No. Filed Patented Assignee METHODS OF ANDAPPARATUS FOR ASSEMBLING ARTICLES 10 Claims, 20 Drawing Figs.

US. Cl 29/429, 29/203, 29/469, 29/592, 29/625, 228/6 Int. Cl ..B23p19/00, HOSk 13/00, B23p 21/00 Field of Search 29/429,

203, 469, 592, 203 (MW), 203 (MM), 203 (P), 625;228/6 [56] ReferencesCited UNITED STATES PATENTS 3,243,180 3/1966 Van Ryn 29/464X 3,465,4359/1969 Steranko 29/469X Primary ExaminerThomas H. Eager Att0rneys-l-l.J. Winegar, R. P. Miller and R. Y. Peters ABSTRACT: Groups of elongatedparamagnetic articles, having headed ends, are aligned with and movedthrough groups of bores in an assembly fixture after which washers areplaced over the ends of the elongated articles. The assembly fixture isinverted and the washers slide along the articles into engagement withthe headed ends of the articles and are held thereagainst when thefixture is returned to an original position. The lower unheaded ends ofthe articles are positioned in holes formed in a wafer after which theelongated articles are released to drop slideably in the holes in thewafers until the washers engage the top surface of the wafer.

Patented April 13, 1971 3,5 74,91 9

4 Sheets-Sheet 5 a 7/5 3 ,/5 as (1/ Y/I/ A/ w 46 3/ /5 ecu 5 a:

#1 g= SH 72 F1 g-sa 1 METHODS OF AND APPARATUS FOR ASSEMBLING ARTICLESBACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates to methods of and apparatus for assembling articles, and moreparticularly, to methods of and apparatus for simultaneously threading aplurality of groups of elongated paramagnetic leads individually throughwashers and then assembling the lead-washer subassemblies to wafers.

2. Prior Art and Technical Considerations In the manufacture of smallelectronic components, such as semiconductor diodes, it is frequentlydesirable to mount the components on support structures which arecommonly referred to as headers. Each header consists of awaferwasher-lead subassembly and a flanged cup-shaped ring to which thesubassembly is brazed by means of a brazing washer. The subassemblyincludes a metallized-ceramic wafer to which one or more paramagnetic,headed leads and small brazing washers are assembled.

Brazing washers are mounted on the leads and then the unheaded ends ofthe leads are inserted through openings provided in the ceramic wafer.Since the openings in the wafer are large enough to pass the elongatedportion of the leads but not the brazing washers or the heads of theleads, the brazing washers are sandwiched between the metallized surfaceof the ceramic wafer and the heads of the leads. When another brazingwasher is added to a flange and a properly oriented subassembly placedon top, the combination can be processed through an appropriate brazingfurnace at the proper temperature for a suitable length of time, tobraze the leads and flange to the metallized-ceramic wafer, thus forminga header.-

Present methods of assembling the leads to the ceramic wafers includemounting the brazing washers on the leads by hand and then threading thelead and washer assemblies individually through the openings in theceramic wafers. This is a relatively slow, laborious, and costlyprocess.

Summary of the Invention Accordingly, an object of this invention is toprovide new and improved methods of an apparatus for subassembling aplurality of groups of elongated articles through individual washers,and for then assembling each group of articles to a wafer.

With these and other objects in mind, this invention contemplatesdropping paramagnetic elongated articles through bores in an assemblyfixture after which individual washers are threaded over the articlesand held in the vicinity of the headed ends of the articles when theassembly fixture is inverted to position the unheaded ends of thearticles in apertures formed in a predetermined pattern in a waferwhereafter the articles are released to drop downwardly until supportedagainst the top surface of the wafer.

More particularly, a mass of elongated paramagnetic articles having oneend headed are held in spaced, parallel relation in a plurality ofgroups in a predetermined pattern in a loading fixture above a pluralityof groups of bores in an assembly fixture. The articles are passedthrough the bores until the headed ends are held by a locking plate toretain the elongated articles in the assembly fixture while the assemblyand loading fixtures are inverted in unison.

Then a tray having a plurality of groups of washers arranged in thepredetermined pattern coincident with the articles is placed below theunheaded ends of the articles. A magnet is positioned above the assemblyfixture to hold the headed ends of the elongated paramagnetic articles apredetermined distance above the locking plate, and against a supportplate which is interposed between the magnet and the locking plate. Inthis way, the lower ends of the elongated articles do not protrude fromthe assembly fixture and bending of the leads is precluded. Moreover,the leads cannot interfere with the alignment of the assembly fixtureand a washer loading tray.

The magnet is then removed and the assembly fixture and the washer trayare vibrated in unison to urge the end of each of the elongated articlesinto a washer. The support plate is replaced with a retaining plate;after which the fixture and tray are inverted to drop the washersthrough the bores of the assembly fixture and against the undersides ofthe heads of the elongated articles. The retaining plate maintains theshank portions of the elongated articles in the washers and theelongated articles in the bores of the assembly fixture, duringinversion of the fixtures. Both the elongated articles and the washersare held in the assembly fixture by the locking plate upon reinversionof the assembly fixture.

A plurality of ceramic wafers, each having a group of openings formedtherein in the predetermined pattern, are aligned with the elongatedarticles in the assembly fixture. The magnet and support plate arerepositioned above the assembly fixture to attract and hold the headedends of the elongated articles against the support plate so that thelower ends of the elongated articles do not protrude from the assemblyfixture and interfere with the positioning and aligning of the ceramicwafers in a loading tray. Then, the magnet is removed and the assemblyfixture and loading tray are vibrated in unison until the end of eachelongated article is moved into one of the openings in the alignedwafers. The support plate is replaced with the retaining plate on theassembly fixture to maintain the unheaded ends of the elongated articlesin the wafer holes; then the assembly fixture and loading tray areinverted in unison and slightly vibrated to urge the wafers to slidedownwardly along the elongated articles and into engagement with theassembly fixture. A second locking plate is used to retain the ceramicwafers in engagement with the assembly fixture when the assembly fixtureis reinverted to the original position.

Then the retaining plate is removed and the support plate and magnet arerepositioned 0n the assembly fixture. The assembly fixture is invertedand then reinverted whereupon the elongated articles are held up againstthe support plate so that the lower ends of the elongated articles donot protrude from the assembly fixture. The assembly fixture is placedover a brazing fixture having openings which are aligned with theelongated members in the assembly fixture. The locking plates are movedslidably to release and drop the articles vertically downward until thewashers and headed ends are supported on the wafers and the wafers aresupported on the brazing fixture.

Other objects, advantages, and features of the invention will beapparent when taken in conjunction with the accompanying drawings.

Brief Description of the Drawings FIG. 1 is an exploded perspective viewof a plurality of headed leads, washers and a ceramic wafer which areassembled together by the principles of the method of this invention toform a header subassembly;

FIG. 2 is a perspective view partially in section of a headersubassembly including one metallized-cerarnic wafer, a plurality ofleads and brazing washers which are assembled by the principles of themethod of the present invention;

FIG. 3A is a perspective view of an assembly fixture which may be usedto practice the steps of the method of this invention to assemble aplurality of the header subassemblies, partially in section to show adetail view of a portion of the assembly fixture with one of a pluralityof guide bores in a body member of the fixture;

FIG. 3B is a detailed perspective view of a portion of a locking plateand showing one of a plurality of keyhole-shaped openings formedtherein;

FIG. 4A is a partial section of a lead loading fixture having a loadingplate with a configuration of openings which coincides with thearrangement of bores in the assembly fixture shown in FIG. 3A, andhaving magnetic facilities for aligning a mass of leads for loading intothe loading plate;

FIG. 4B is a partial section of the lead loading fixture shown in FIG.4A with the leads drawn through the openings in the loading plate;

FIG. 5A is a partial cross-sectional view taken along line 5-5 in FIG.3A and showing the leads in the loading plate ositioned below theassembly fixture with the leads aligned with the bores in the assemblyfixture;

FIG. 5B is the same partial cross-sectional view of the assembly fixturein an inverted position and showing the leads passed through the boresin the assembly fixture until the headed ends thereof engage a retainingplate positioned below the body member of the assembly fixture;

FIG. 5C is the same partial cross-sectional view of the assemblyfixture, reinverted, with the lead-loading plate removed and showing theleads held in the assembly fixture by a locking plate;

FIG. 6A is a partial cross-sectional view, taken along line 5-5 of FIGS.3A, of a tray of washers positioned below the assembly fixture with eachof the washers aligned with one of the bores in the body member of theassembly fixture;

FIG. 6B is the same partial cross-sectional view of the assembly fixtureand showing the lower ends of the leads inserted into the washers in thetray;

FIG. 6C is the same partial cross-sectional view showing the assemblyfixture in an inverted position with the washers having descendedthrough the bores in the body member and now in engagement with theheaded ends of the leads;

FIG. 7 is a partial cross section, taken along line 5-5 of FIG.

3A, showing the leads with the washers threaded thereon retained by alocking plate in the assembly fixture;

FIG. 8A is a partial cross-sectional view, taken along line 5-5 in FIG.3A, of a tray holding a plurality of ceramic wafers positioned below theassembly fixture with each of the wafers aligned with a group of theleads, which are held above the wafer by a magnet;

FIG. 8B is the same partial cross-sectional view of FIG. 8A showing themagnet removed and the leads in a descended position with the end of theleads inserted in openings in the ceramic wafer;

FIG. 8C is the same partial cross-sectional view as in FIG. 8A showingthe assembly fixture and wafer tray in an inverted position with thewafer having dropped through an opening in a locking plate and now inengagement with the body member of the assembly fixture;

FIG. 9 is a plan view of one cavity of the ceramic-wafer loading tray asviewed along line 9-9 of FIG. 8A;

FIG. 10A is a partial cross-sectional view, taken along line 5-5 of FIG.3A, of the assembly fixture showing leads held in a suspended positionby the magnet above a brazing fixture;

FIG. 10B is a partial cross-sectional view of the assembly fixture shownin FIG. 10A with the magnet removed and the leads and washers descendedinto engagement with the wafers; and

FIG. 10C shows the wafer-lead-washer subassembly moved from the assemblyfixture and seated in the brazing fixture.

DETAILED DESCRIPTION General Referring to FIG. 1, four nonmagneticwashers 11 are assembled on four paramagnetic leads 12 having headedends 15, and then each of the leads is inserted in an aperture 13 in aceramic wafer 14. The ceramic wafer 14 has metallized surfaces 16, whichhave been plated, and a notch 17 formed in a peripheral edge thereof ina predetermined relation to the pattern of the apertures 13 and themetallized surfaces. The wafer 14 together with the leads l2 and washers11 are referred to as a subassembly, designated generally by numerals18, (see FIG. 2) which is subsequently positioned on anothersubassembly, which includes a flange 82 (see FIG. 10A) and brazingwasher 83 (see FIG. 10A), in preparation for a brazing operation.

Assembly Fixture Referring now to FIG. 3A, an assembly fixture,designated generally by the numerals 19, includes a transfer or bodymember 20 to which side members 22 are fastened. The body member 20includes a lower portion 21 and an upper portion 21, which are fastenedtogether and which are formed with a plurality of aligned bores 23 and23, respectively, arranged in patterns of four, aligned with the leads12 in the subassembly 18 (see FIG. 5A). The bores 23 and 23' are formedwith a small diameter portion 24 (see FIG. 5A) which opens to a bottomsurface of the bottom portion 21 of the body member 20 and a smalldiameter portion 24' which opens to a top surface of the upper portion21' of the body member. The small diameter portions 24 and 24' arelarger than the diameter of the headed end 15 of the lead 12 and of thewasher 11. Also, the smaller diameter portions 24 and 24 are joined tothe bores 23 and 23 by tapered sections 26 and 26', respectively (seeFIG. 5A). The tapered sections 26 and 26' and smaller diameter portions24 and 24 accurately locate the washers 11 and leads 12 while permittingthe washers and leads with moderate camber to slide through the boreswithout binding to the walls of the bores.

In order to retain the leads 12 within the bores 23-23' of the bodymember 20, an upper locking plate 27 is slideably mounted in uppergrooves 28 formed in the side members. The upper locking plate 27 isformed with a plurality of groups of keyhole-shaped openings 29 (seeFIG. 38) having circular portions 31 and slotted portions 32. Thelocking plate 27 is initially positioned so that circular portions 31 ofthe keyhole openings are aligned with the bores 23-23' in the bodymember 20. The circular portions 31 of the keyhole openings 29 areslightly larger than the headed ends 15 of the leads l2 and the washers11. The smaller dimension of the slotted portions 32 of the keyholeopenings 29 is less than the diameter of the headed end 15 of the leads12 or the washers II, but slightly greater than the diameter of theelongated portion of the leads. The upper locking plate 27 may be movedslideably in either direction (see FIG. 3A) to align either the circularportion 31 or the slotted portion 32 of the keyhole-shaped openings 29with the bores 23-23.

In order to prevent the leads 12 from dropping out of the fixture whenthe fixture I9 is inverted during the method of practicing thisinvention, a retaining plate 33, having four ears 34 projectingtherefrom, is secured on the top of the assembly fixture 19 by fourtongues 36 which are formed integrally with the side members 22. Theretaining plate 33 may be removed and replaced as needed by sliding theretaining plate far enough to the right as viewed in FIG. 3A to clearthe tongues 36. v

The raising of the leads 12 in the bores 23-23' is accomplished with theassistance of a support plate 37, and a magnet 38 in engagement with thesupport plate. The support plate 37 is formed with four ears 39 whichare positioned under the tongues 36 and which permit the support plateto be removed and replaced along with the magnet 38, or retained on topof the assembly fixture 19. Additionally, the support plate 37 is formedso that a lower surface thereof is spaced above the upper locking plate27 a distance greater than the upper surface of the retaining plate 33.Hence, the distance between the upper locking plate 27 and the supportplate 37, when the support plate is in position, is greater than thatbetween the upper locking plate 27 and the retaining plate 33 when theretaining plate is in position.

A second or lower locking plate 41 is used in the manipulation of thewafers 14. The lower locking plate 41 has slotted keyhole-shapedopenings 42 formed therein and is mounted slidably in lower grooves 43cut in the side members 22. The center of a circular portion 44 of theopenings 42, is aligned with a center of each cluster of four of thebores 23-23 in the body member 20. Also, the circular portion 44 of theopenings 42 is slightly larger than the diameter of the ceramic wafersl4, and the smaller dimension of a slotted portion 46 is slightlygreater than the diameter of the elongated shank portion of a lead 12.

Loading Fixture Prior to assembling the header subassembly 18 in theassembly fixture 19, it is necessary to preload a mass of the leads 12,by methods known in the art such as a vibratory technique into a loadingfixture 51 (see FIG. 4A). Referring now to FIGS. 4A and 4B, the loadingfixture 51 includes a base or load plate 52 having a plurality of bores53, a shuttle plate 54, having openings 56, and support rails 57. Thebores 53 and openings 56 in the base plate 52 and the shuttle plate 54,respectively, are congruent with the bores 23-23 in the body member ofthe assembly fixture 19. Also, the openings 53 and 56 in the base plate52 and shuttle plate 54, respectively, are larger than the diameter ofthe elongated portion of the lead 12. Moreover, the openings 56in theshuttle plate 54 are less than twice the diameter of the lead 12 so thatonly one lead may be positioned in each opening.

In loading the leads 12, a random mass of leads is placed in a boxlikeenclosure 58 constructed of nonmagnetic material, e.g., plastic oraluminum. The loading fixture 51 which includes the shuttle plate 54 isplaced over the enclosure 58 to trap the leads 12 between the enclosureand the shuttle plate. Then, the loading fixture 51 and enclosure 58 areinverted as a unit and positioned in a magnetic field establishedbetween upper and lower magnets 61 and 59, as shown in FIGS. 4A and 48,with the support rails 57 of the loading fixture 51 resting on the lowermagnet 59. The enclosure 58 and the loading fixture 51 are moved inunison back and forth, horizontally, by imparting vibratory motionthereto until the mass of elongated paramagnetic leads are disentangledand then supported in parallel, spaced relation along the magnetic linesof forces established between the magnets 59 and 61. Moreover, since thedistance between the leads 12 and the magnet 59 is less than thedistance between the leads and the magnet 61, the leads are attracted tothe lower magnet 59.

The leads 12 are confined in the space between the enclosure 58 and theplate 54 to prevent the formation of chains of leads which couldundesirably bridge the gap between the upper and lower magnets 59 and 61and prevent all the leads 12 from migrating toward the lower magnet 59.The sidewalls of the enclosure 58 also prevents the leads 12 frommigrating laterally due to repulsive forces of like magnetic poles atopposite ends of the leads when a large quantity of leads are placed inthe enclosure 58.

Initially, the shuttle plate 54 is positioned, as shown in FIG. 4A, toprevent the leads 12 from entering prematurely the openings 53 in baseplate 52 of the loading fixture 51 and to permit untangling andalignment of the leads in the magnetic field between the shuttle plateand the enclosure 58. The openings 56 in the shuttle plate 54 arecountersunk so that the ends of the leads l2 tend more easily to locatein these openings. A cluster of the aligned leads 12 congregate abouteach of the openings 56 in the shuttle plate 54. Moreover, since theentrance of the openings 56 in the shuttle plate 54 are beveled, theleads 12 may pivot due to the movement of the mass of the leads.Otherwise, if one end of a lead 12 were to jam in an opening in theshuttle plate 54 while the other end was forced to move by a mass ofclustered leads therearound during the back and forth motion of thefixture 51 and enclosure 58, the lead, restrained at one end, would bendand be damaged.

An initial group of the leads 12 is urged through the bores 53 andopenings 56in the loading fixture 51 by a combination of gravitationaland magnetic forces. After the leads 12 are untangled and aligned withthe magnetic .lines of force with leads positioned in random holes 56 inthe shuttle plate 54. the shuttle plate is moved slideably over the baseplate 52 until the openings 56 in the shuttle plate are aligned with thebores 53 in base plate 52. The leads 12 are attracted toward the lowermagnet 59 to move the lower ends of the leads which are already in theholes 56 of the shuttle plate into the loading fixture 51 (see FIG. 4B)so that the headed ends 15 are supported on a top surface of the shuttleplate 54. Further horizontal oscillation of the loading fixture 51together with the enclosure 58, pass the elongated shanks of the leads12 onto the countersunk portions of the unfilled holes and through theloading fixture 51 until the heads of the leads engage the shuttle plate54.

The loading fixture 51, now loaded with the leads 12 is withdrawn alongwith the enclosure 58 from the magnetic field between the magnets 59 and61. Since the openings 56in the shuttle plate 54 are smaller than thediameter of the headed ends of the leads 12, the leads do not fallthrough the loading fixture 51 when the loading fixture is withdrawnfrom between the magnets.

As an alternate embodiment, a backup plate 67 may be added to permitloading articles which do not have headed ends 15 by positioning thebackup plate close enough to the bottom of the loading fixture 51 toprevent the articles from passing therethrough. Otherwise articles 12without heads would not be trapped in the assembly fixture ashereinbefore described.

In order to assume an orderly transfer of the leads 12 from the loadingfixture to the assembly fixture, an alignment plate 62 is positioned inengagement with the shuttle plate 54 so that locating pins 63 on thealignment plate are received in cavities 64 in the shuttle plate (seeFIG. 5A). In this way a plurality of stepped bores 66 in the alignmentplate 62 are aligned with the bores 53 in the base plate 52 of theloading fixture 51 and the bores 23-23' in the assembly fixture 19 toguide the leads 12 when the leads are moved from the loading fixtureinto the assembly fixture.

Method of Assembly Referring now to FIGS. 5A, 5B, and 5C, the fixture51, with the enclosure 58 removed, is positioned beneath the assemblyfixture 19 with the support plate 37 inserted above the body member 20and with the bores 53 and openings 56 in the loading fixture alignedwith the bores 23-23 in the assembly fixture. The circular portions ofthe openings in the upper and lower locking plates 27 and 41,respectively, are also aligned with the bores 23 and 23 in the assemblyfixture 19 and the bores 53 and openings 56 in the loading fixture 51 topermit free passage therethrough of the leads 12.

The fixtures 19 and 51 are inverted, in un son, to permit the leads 12to move through the bores 66 in the alignment plate 62 and the fixture19 under the urging f gravitational force until the headed ends 15 seatagainst the support plate 37 as shown in FIG. 5B. The magnet 38 is thenplaced in engagement with the support plate in preparation for the nextsequence of steps. The loading fixture 51 is removed and the upperlocking plate 27 is moved to the left, as viewed in FIG. SE, to shiftthe slotted portion 32 of the keyhole openings 29 over the headed ends15 of the leads 12.

Referring to FIG. 5C, it can be seen that if it were necessary tointerrupt the operation at this point, and the fixture reinverted, theleads 12 would drop away from the support plate 37 until the headed ends15 engage the locking plate 27. Since the headed ends 15 cannot passthrough the slotted portions 32 of the keyhole openings 29, the leads 12are retained in the fixture. However, in the uninterrupted practice ofthe method of this invention, the assembly fixture 19 is retained in aninverted position and the magnet 38 is placed in engagement with thesupport plate 37 to hold the leads 12 up against the bottom of thesupport plate 37 when the assembly fixture 19 is reinverted, as shown inFIG. 6A, in preparation for the threading of the washers 11 on theleads.

In the next sequence of steps in carrying out the method of thisinvention, as shown in FIGS. 6A, 6B, and 6C, washers 11 are threadedover the shank portions of the leads 12. While the leads are held in theposition shown in FIG. 6A, a tray 68 having stepped bores 69, is loadedby manual and vibratory techniques to seat a washer 11 on an annularsurface 71 of each of the stepped bores. Then the tray 68 is positionedbeneath the assembly fixture 19 with the stepped bores 69 aligned withthe bores 23-23 in the assembly fixture. The magnet 38 and support plate37 are removed from the assembly fixture 19 whereupon the leads 12 dropvertically to move the ends of the leads l2 partially through thewashers 11 in the washer tray 68 (see FlG. 6B). The assembly fixture 19and the washer tray 68 are vibrated in unison while maintaining thealigned relationship therebetween until all the leads 12 are partiallythreaded through the washers 11. Because the upper locking plate 27 ispositioned with the slotted portions 32 of the keyhole slots 29 alignedwith the bores 23- 23, the leads 12 do not drop all of the way throughthe assembly fixture 19, but remain suspended by the heads engaging theupper locking plate 27.

Then the retaining plate 33 is positioned above the locking plate 27 inpreparation for the assembly of the washers 11 on the shank portions ofthe leads 12. The assembly fixture 19 and the tray 68 are inverted inunison and the locking plate 27 is shifted to the right, as viewed inH0. 6C, to align the circular portions 31 of the keyhole openings 29with the bores 23-23 in the body member 20. The washers 11 dropvertically and slide along the shank portions of the leads 12 throughthe keyhole openings 42 in the lower (now upper) locking plate 41,through the bores 23-23 in the body member 20, and through the keyholeopenings 29 in the upper (now lower) locking plate 27 into engagementwith the headed ends of the leads 12 as shown in FIG. 6C. When thewashers 11 are in engagement with the heads of the leads 12, the upper(now lower) locking plate 27 is moved slidably to the left as viewed inFIG. 6C to trap the washers and the headed ends of the leads between theretaining plate 33 and the plate 27. The tray 68 is then removed and theassembly fixture 19 reinverted whereupon the leads 12 and washers dropvertically until washers 11 engage and are supported on the lockingplate 27 (see FIG. 7).

Referring now to FIG. 8A, the ceramic wafers 14 are loaded into a tray72 by vibratory techniques well known in the art. The tray 72 has aplurality of cavities 73, each of which is aligned with the center of acluster of the bores 23-23 in the body member 20. A pin 74 is pressfitted in the tray 72 astride the edge of each of the cavities 73 (referto HO. 9) to cooperate with the notches 17 in the ceramic wafers 14 toorient the openings 13 in the wafers with bores 76 formed in theceramic-wafer tray 72. The bores 76 in the tray 72 which open into thecavities 73, are dimensioned to receive the elongated portions of theleads [2 and are aligned with the bores 23-23' in the body member of theassembly fixture 19. In addition, ports 77 are formed in the tray 72 andopen into the centers of the cavities 73. The ports 77 are connected toa source of vacuum (not shown) to apply a vacuum to the underside ofeach of the ceramic wafers 14. The vacuum retains the ceramic wafers 14in the cavities 73 after the wafers have been vibrated into position inthe cavities.

In the next sequence of steps, each of the wafers 14 is threaded overthe end portions of a group of the leads 12. Referring now to FIG. 8A,the retaining plate 33 is replaced with the support plate 37 and magnet38. The assembly fixture 19 is inverted and the leads 12 are urged bygravitational and magnetic forces into engagement with the plate 37 tohold the leads 12 above a lower surface of the locking plate 41 when theassembly fixture 19 is reinverted. Then the tray 72 can be positionedbeneath and aligned with the assembly fixture 19 without bending anyleads. Then the magnet 38 is removed and the assembly fixture l9 and thetray 72 are vibrated in unison to urge the leads 12 into and through theapertures 13 in the ceramic wafers 14. The leads 12 are arrested whenthe heads of the leads engage the locking plate 27. The plate 37 isremoved and replaced with the retaining plate 33 (see FlG. 88).Subsequently, the assembly fixture 19 and the ray 72 are inverted as aunit, whereupon the ceramic wafers 14 slide along the leads 12 and dropthrough the keyhole openings 42 in the locking plate 41 until the wafersare supported on a surface of the portion 21 of the body member 20 (seeFIG. 8C). When all of the ceramic wafers 14 are supported on the bodymember 20, the locking plate 41 is moved to the left as viewed in FIG.8C to misalign the circular portions 44 of the keyhole openings 42 withthe ceramic wafers 14 to trap the ceramic wafers between the lockingplate 41 and the body member 20 ofthe assembly fixture 19.

Next, the leads 12 are assembled to the wafers 14 to support the headedends 15 of the leads on the wafers. As can best be seen in FIGS. 10A,10B, and 10C, the tray 72 is removed and the assembly fixture 19 isreinverted. The retaining plate 33 is replaced by the plate 37 and themagnet 38 so that the leads 12 can be attracted to and held inengagement with the underside of the magnet plate 37. In this position,the leads 12 protrude through the ceramic wafers 14 but do not protrudebelow locking plate 41 to facilitate alignment with a brazing fixture 78without bending any leads. If necessary, the assembly fixture 19 mayagain be inverted to apply gravitational forces to the leads to insurethat the leads are in engagement with the support plate 37, after whichthe fixture 19 is reinverted to the position shown in FIG. 10A.

The brazing fixture 78 has a plurality of bores 79 which are alignedwith the bores 23-23 of the body member 20 to receive the leads 12. Thebores 79 open to a plurality of larger cavities 81, the centers of whichare coincident with the centers of the clusters of bores 23-23'.Moreover, each of the cavities 81 is preloaded with a flange 82 and abrazing preform 83. The brazing fixture 78, which is made of materialsuitable for use in high temperature furnaces, is aligned with theassembly fixture 19, and the upper locking plate 27 is shifted to theright as viewed in FIG. 10B to align the circular portions 31 of thekeyhole openings 29 with the bores 23-23' and permit the washers 11 andthe leads 12 to drop through the body members 20 of the assembly fixture19 until the washers 11 engage the ceramic wafers 14. Then the lowerlocking plate 41 is shifted to the right, as viewed in FIG. 108, toalign the circular portions 44 of the keyhole-shaped openings 42 withthe cavities 81 in the brazing fixture 78. The subassemblies 18,consisting of the washers 11, leads 12, and ceramic wafers 14 drop ontothe brazing fixture 78 to complete the assembly of the units and thetransfer of the units to the brazing fixture as shown in FIG. 10C. Theassembled units, each consisting of flange 82, preform 83, wafer 14,washers 11, leads 12, are now placed in a furnace to bond thesubassembly 18 to the flange and the leads 12 to the wafer 14.

lclaim: I

1. ln a method of assembling elongated articles to discshaped articleseach having an aperture formed therethrough:

supporting an array of said elongated articles in parallel relationshipwith each other;

positioning a like array of said disc-shaped articles below the ends ofsaid elongated articles; inserting the ends of said elongated articlesinto said apertures in said disc-shaped articles; and

inverting said elongated articles and said disc-shaped articles to slidesaid disc-shaped articles along said elongated articles.

2. A method of assembling a paramagnetic pin having a headed end througha washer and into a aperture formed in an article, which comprises:

magnetically holding the headed end with the pin depending toward andaligned with the washer;

releasing the magnetic force to drop the pin into the aperture;inverting the pin to seat the washer against the headed end; againinverting the assembled pin and washer; and again magnetically holdingthe head with the pin depending toward and aligned with the aperture inthe article;

supporting the washer in a position spaced from the headed end adistance greater than the distance between the depending end of the pinand the aperture;

releasing the magnetic force to drop the pin through the supportedwasher to move the depending end into the aperture; and then releasingthe washer todrop the pin into the aperture and move the washer intoengagement with the article.

3. ln a method of assembling a group of washers and a wafer with a likegroup of holes therethrough onto shanks of a group of headed leads:

supporting the headed leads with the shanks thereof dependingdownwardly;

positioning a group of washers in alignment with said shanks of saidleads;

releasing said headed leads to move depending ends of the shankspartially through said washers;

inverting the leads and washers to move the washers along the shanks toengage the heads on the leads;

repositioning the leads and washers to support the heads with the shanksdepending downwardly while holding the washers in the vicinity of theheads; positioning said wafer below said leads with the holes thereinaligned with the depending ends of the shanks;

releasing the leads to move the heads into engagement with the washerswhile the ends of the shanks move through the aligned holes in thewafer;

inverting the washers, leads, and wafer to move the wafer apredetermined distance along the group of the leads; reinverting thewashers, leads, and wafer; and

releasing the washers to drop the shanks through the wafer and move thewashers into engagement with the wafer.

4. In a method of assembling each of a group of leads each having aheaded end and an unheaded end, through a washer and then with anarticle having a group of apertures arranged in a predetermined pattern:

supporting said group of leads in parallel relationship with each otherand arranged in said predetermined pattern, with said headed endsoriented upwardly;

positioning a group of washers arranged in said predetermined patternbelow the unheaded ends of said leads with each of said washers alignedwith one of said leads;

releasing said leads to move the unheaded ends of said leads into saidwashers;

inverting said leads and said washers to slide said washers along saidleads and into engagement with said headed ends;

reinverting said leads while holding the leads with said headed endsaligned in a plane;

supporting the washers spaced a predetermined distance from the headedends of the leads;

placing said article below the unheaded ends of said leads a distanceless than said predetermined distance while aligning said apertures withsaid leads; releasing said leads to move the headed ends of the leadsthrough said predetermined distance into engagement with the washers andmove the unheaded ends of the leads into the apertures in said article;and v releasing said washers to move said washers and leads in unisonrelative to said article to thread said leads through said apertures andsupport said washers and said leads against said article.

5. A method of assembling a group of headed leads, a group of washers,and a pair of members having a pattern of apertures formed therethrough,each of said apertures being larger than the shank of a lead but smallerthan the head of a lead;

supporting a group of leads in a pattern corresponding to said patternof apertures with the unheaded ends of the leads extending downwardly;positioning a group of washers in a pattern corresponding to the patternof leads beneath and spaced from said leads; releasing the leads topartially drop through said washers; inverting the washers and leads toslide the washers against the headed ends of the leads; reinverting theleads;

supporting the washers and the leads with the headed ends apredetermined distance from the washers;

supporting a first member with the apertures aligned with the unheadedends of the leads and at a distance which is less than saidpredetermined distance; releasingthe leads to drop said unheaded endsinto said apertures of said first member;

supporting said washers and said headed ends to retain the leadspartially extending through the apertures in said first member;

supporting a second member with the apertures aligned with saidpartially extending leads;

releasing said washers and leads to drop said leads through saidapertures in the first member into the apertures in said second memberwhere the leads are maintained in position by engagement of the washerswith the top surface of said first member; and

releasing said first member to advance into engagement with the secondmember and move said leads through said apertures.

6. In a method of assembling a plurality of predetermined groups ofparamagnetic leads, each lead having a headed end and an unheaded end,with a plurality of groups of washers and a plurality of wafers eachhaving a predetermined pattern of apertures:

magnetically positioning and then supporting a plurality of groups ofsaid leads in patterns, each of which corresponds to said predeterminedpattern, in an initial position with the longitudinal axes of said leadsparallel and the headed ends oriented upwardly;

moving and then holding said leads to align the heads of said leads in aplane;

placing a plurality of groups of washers, each arrayed in saidpredetermined pattern, below and aligned with the unheaded ends of saidleads;

releasing said leads to drop and move the lower unheaded ends of theleads through said washers;

inverting said leads to slide the washers along said leads and intoengagement with the headed ends thereof; magnetically holding saidheaded ends in a plane; reinverting said leads to the initial positionto slide said washers along said leads;

supporting said washers a predetermined distance out of engagement withsaid headed ends;

aligning a plurality of wafers a distance less than said predetermineddistance beneath the unheaded ends of said leads with the apertures insaid wafers aligned with said unheaded ends of said leads;

releasing said leads to drop said prede ermined distance to support saidheaded ends in ezgagement with said washers and to move said lowerunheaded ends through said apertures in said wafers;

inverting said leads and wafers to slide said wafers along said leads;

holding said wafers spaced from the unheaded ends of the leads; and

releasing said washers to drop said washers and said leads intoengagement with said wafers.

7. A method of loading an array of paramagnetic pins in a fixture forsubsequent processing, each of said pins having a headed end and anunheaded end, wherein the fixture comprises a first horizontal platehaving a first array of holes therethrough and a second plate overlyingthe first plate and having a second, like array of holes therethrough,each of said holes in the second plate being smaller than the headed endof a pin, which comprises:

moving one plate relative to the other to move the holes out ofalignment;

placing a mass of paramagnetic pins on the second plate;

applying a magnetic field transversely of the plates to verticallysuspend the pins with lower ends thereof bearing against the secondplate;

imparting relative movements between said plates and said suspended pinsto move the unheaded ends of certain of said pins into the holes in thesecond plate; and

moving one plate relative to the other to move the holes into alignmentto permit those pins positioned in the holes in the second plate to passthrough the holes in the first plate and be retained by the headed endsengaging the top surface of the second plate.

8. in an arrangement of apparatus for assembling a washer onto a shankof a pin having a headed end:

a frame having a pair of spaced vertical end plates;

a first plate having a slot for receiving the shank of the pin andsupporting the headed end, said slot being narrower than the diameter ofthe headed end and the washer;

means for slideably supporting said first plate between said end plateswith the shank of the pin extending in a downward direction;

means for lifting the pin in the slot and then releasing the means forsupporting a washer in the space vacated by the lifted pin and inposition to receive the released pin; and

a second plate slideably mounted between said end plates for retainingthe pin in the slot upon inversion of the frame, said first plate havinga bore extending therethrough at one end of said slot, said bore beinglarger than the washer and positioned by sliding the first plate to passsaid washer along said shank into engagement with said headed end;

9. In an assembly fixture for assembling a plurality of groups ofparamagnetic leads supported in parallel spaced relation, each of saidleads having headed and unheaded ends, with a plurality of groups ofwashers and then with a plurality of wafers each having a predeterminedpattern of apertures:

a transfer member having a plurality of groups of bores formedtherethrough for guiding said leads, each of said groups arranged insaid predetermined pattern;

means movably mounted for magnetically supporting a group of said leadsin an initial position to align said headed ends in a plane with saidunheaded ends depending downwardly into said groups of bores;

a locking plate interposed between said supporting means and saidtransfer member and having a plurality of groups of keyhole-shapedopenings formed therein and arranged in said predetermined pattern, witha circular portion of each of said openings aligned initially with oneof the bores in said transfer member for receiving said groups of leads,said keyhole opening having a slotted portion which is narrower than thediameter of the headed end and the washer;

means mounting said locking plate for sliding movement to positionslotted portions of said keyhole openings over said bores in saidtransfer member and to confine said washers and said headed ends betweensaid locking plate and said supporting means;

means for holding said plurality of groups of washers below the unheadedends of said leads with each of said groups of washers arranged in saidpredetermined pattern and with each of said washers aligned with one ofsaid bores in said transfer member;

a second locking plate, having a plurality of openings formed therein,said second locking plate interposed between said holding means and saidtransfer member for guiding said wafers into engagement with a bottomsurface of said transfer member when said fixture is inverted, each ofsaid openings in said plate having a slot extending radially therefrom,said slot being narrower than the diameter of a wafer; and

means mounting said plate for sliding movement to lock said wafersagainst said transfer member and to permit one lead of each of saidgroups to be received in one slot before said fixture is returned to theinitial position.

10. In a fixture for assembling a plurality of groups of paramagneticleads, each of said leads having headed and unheaded ends, with aplurality of groups of washers, and then with a plurality of wafers,each having a predetermined pattern of apertures, said leads heldinitially in parallel, spaced relation with said headed endsorientedupwardly:

a transfer member having a plurality of groups of bores formedtherethrough, each of said groups having said bores arranged in saidpredetermined pattern;

magnetic means for supporting said leads with said headed ends alignedin a plane and with said unheaded ends received in said bores in saidtransfer member;

a first locking plate interposed between said magnetic means and saidtransfer member and having a plurality of groups of keyhole-shapedopenings formed therein and arrayed in said predetermined pattern with acircular portion of said openings aligned with the bores in saidtransfer member, and with slotted portions of said openings beingnarrower than said washers and said unheaded ends;

means mounting said first locking plate for sliding movement to positionthe slotted portions of said keyhole openings over said bores in saidtransfer member and to confine said washers and said headed ends betweensaid locking plate and said magnetic means;

means for holding said plurality of groups of wafers arranged in saidpredetermined patterns below the unheaded ends of said leads with eachof said washers aligned with one of said leads;

a second locking plate having a plurality of openings and interposedbetween said wafers and said transfer member for passing said wafers toslide along the unheaded ends of said leads and against the bottomsurface of said transfer member when said fixture is inverted, each ofsaid openings aligned initially with one of said groups of bores in saidtransfer member and having a slot formed therein radially extendingtherefrom, each of said slots being narrower than the wafer and largerthan the diameter of the unheaded end of the lead;

a retaining plate slideably mounted between said magnetic means and saidfirst locking plate for engaging and holding the leads in the transfermember when said fixture is inverted; and

means for slideably mounting said second locking plate to shift saidsecond locking plate to lock said wafers against said transfer memberand to permit one lead of each of said groups of leads to be received inone slot before said fixture is returned to said initial position.

1. In a method of assembling elongated articles to disc-shaped articleseach having an aperture formed therethrough: supporting an array of saidelongated articles in parallel relationship with each other; positioninga like array of said disc-shaped articles below the ends of saidelongated articles; inserting the ends of said elongated articles intosaid apertures in said disc-shaped articles; and inverting saidelongated articles and said disc-shaped articles to slide saiddisc-shaped articles along said elongated articles.
 2. A method ofassembling a paramagnetic pin having a headed end through a washer andinto a aperture formed in an article, which comprises: magneticallyholding the headed end with the pin depending toward and aligned withthe washer; releasing the magnetic force to drop the pin into theaperture; inverting the pin to seat the washer against the headed end;again inverting the assembled pin and washer; and again magneticallyholding the head with the pin depending toward and aligned with theaperture in the article; supporting the washer in a position spaced fromthe headed end a distance greater than the distance between thedepending end of the pin and the aperture; releasing the magnetic forceto drop the pin through the supported washer to move the depending endinto the aperture; and then releasing the washer to drop the pin intothe aperture and move the washer into engagement with the article.
 3. Ina method of assembling a group of washers and a wafer with a like groupof holes therethrough onto shanks of a group of headed leads: supportingthe headed leads with the shanks thereof depending downwardly;positioning a group of washers in alignment with said shanks of saidleads; releasing said headed leads to move depending ends of the shankspartially through said washers; inverting the leads and washers to movethe washers along the shanks to engage the heads on the leads;repositioning the leads and washers to support the heads with the shanksdepending downwardly while holding the washers in the vicinity of theheads; positioning said wafer below said leads with the holes thereinaligned with the depending ends of the shanks; releasing the leads tomove the heads into engagement with the washers while the ends of theshanks move through the aligned holes in the wafer; inverting thewashers, leads, and wafer to move the wafer a predetermined distancealong the group of the leads; reinverting the washers, leads, and wafer;and releasing the washers to drop the shanks through the wafer and movethe washers into engagement with the wafer.
 4. In a method of assemblingeach of a group of leads each having a headed end and an unheaded end,through a washer and then with an article having a group of aperturesarranged in a predetermined pattern: supporting said group of leads inparallel relationship with each other and arranged in said predeterminedpattern, with said headed ends oriented upwardly; positioning a group ofwashers arranged in said predetermined pattern below the unheaded endsof said leads with each of said washers aligned with one of said leads;releasing said leads to move the unheaded ends of said leads into saidwashers; inverting said leads and said washers to slide said washersalong said leads and into engagement with said headed ends; reinvertingsaid leads while holding the leads with said headed ends aligned in aplane; supporting the washers spaced a predetermined distance from theheaded ends of the leads; placing said article below the unheaded endsof said leads a distance less than said predetermined distance whilealigning said apertures with said leads; releasing said leads to movethe headed ends of the leads through said predetermined distance intoengagement with the washers and move the unheaded ends of the leads intothe apertures in said article; and releasing said washers to move saidwashers and leads in unison relative to said article to thread saidleads through said apertures and support said washers and said leadsagainst said article.
 5. A method of assembling a group of headed leads,a group of washers, and a pair of members having a pattern of aperturesformed therethrough, each of said apertures being larger than the shankof a lead but smaller than the head of a lead; supporting a group ofleads in a pattern corresponding to said pattern of apertures with theunheaded ends of the leads extending downwardly; positioning a group ofwashers in a pattern corresponding to the pattern of leads beneath andspaced from said leads; releasing the leads to partially drop throughsaid washers; inverting the washers and leads to slide the washersagainst the headed ends of the leads; reinverting the leads; supportingthe washers and the leads with the headed ends a predetermined distancefrom the washers; supporting a first member with the apertures alignedwith the unheaded ends of the leads and at a distance which is less thansaid predetermined distance; releasing the leads to drop said unheadedends into said apertures of said first member; supporting said washersand said headed ends to retain the leads partially extending through theapertures in said first member; supporting a second member with theapertures aligned with said partially extending leads; releasing saidwashers and leads to drop said leads through said apertures in the firstmember into the apertures in said second member where the leads aremaintained in position by engagement of the washers with the top surfaceof said first member; and releasing said first member to advance intoengagement with the second member and move said leads through saidapertures.
 6. In a method of assembling a plurality of predeterminedgroups of paramagnetic leads, each lead having a headed end and anunheaded end, with a plurality of groups of washers and a plurality ofwafers each having a predetermined pattern of apertures: magneticallypositioning and then supporting a plurality of groups of said leads inpatterns, each of which corresponds to said predetermined pattern, in aninitial position with the longitudinal axes of said leads parallel andthe headed ends oriented upwardly; moving and then holding said leads toalign the heads of said leads in a plane; placing a plurality of groupsof washers, each arrayed in said predetermined pattern, below andaligned with the unheaded ends of said leads; releasing said leads todrop and move the lower unheaded ends of the leads through said washers;inverting said leads to slide the washers along said leads and intoengagement with the headed ends thereof; magnetically holding saidheaded ends in a plane; reinverting said leads to the initial positionto slide said washers along said leads; supporting said washers apredetermined distance out of engagement with said headed ends; aligninga plurality of wafers a distance less than said predetermined distancebeneath the unheaded ends of said leads with the apertures in saidwafers aligned with said unheaded ends of said leads; releasing saidleads to drop said predetermined disTance to support said headed ends inengagement with said washers and to move said lower unheaded endsthrough said apertures in said wafers; inverting said leads and wafersto slide said wafers along said leads; holding said wafers spaced fromthe unheaded ends of the leads; and releasing said washers to drop saidwashers and said leads into engagement with said wafers.
 7. A method ofloading an array of paramagnetic pins in a fixture for subsequentprocessing, each of said pins having a headed end and an unheaded end,wherein the fixture comprises a first horizontal plate having a firstarray of holes therethrough and a second plate overlying the first plateand having a second, like array of holes therethrough, each of saidholes in the second plate being smaller than the headed end of a pin,which comprises: moving one plate relative to the other to move theholes out of alignment; placing a mass of paramagnetic pins on thesecond plate; applying a magnetic field transversely of the plates tovertically suspend the pins with lower ends thereof bearing against thesecond plate; imparting relative movements between said plates and saidsuspended pins to move the unheaded ends of certain of said pins intothe holes in the second plate; and moving one plate relative to theother to move the holes into alignment to permit those pins positionedin the holes in the second plate to pass through the holes in the firstplate and be retained by the headed ends engaging the top surface of thesecond plate.
 8. In an arrangement of apparatus for assembling a washeronto a shank of a pin having a headed end: a frame having a pair ofspaced vertical end plates; a first plate having a slot for receivingthe shank of the pin and supporting the headed end, said slot beingnarrower than the diameter of the headed end and the washer; means forslideably supporting said first plate between said end plates with theshank of the pin extending in a downward direction; means for liftingthe pin in the slot and then releasing the pin; means for supporting awasher in the space vacated by the lifted pin and in position to receivethe released pin; and a second plate slideably mounted between said endplates for retaining the pin in the slot upon inversion of the frame,said first plate having a bore extending therethrough at one end of saidslot, said bore being larger than the washer and positioned by slidingthe first plate to pass said washer along said shank into engagementwith said headed end.
 9. In an assembly fixture for assembling aplurality of groups of paramagnetic leads supported in parallel spacedrelation, each of said leads having headed and unheaded ends, with aplurality of groups of washers and then with a plurality of wafers eachhaving a predetermined pattern of apertures: a transfer member having aplurality of groups of bores formed therethrough for guiding said leads,each of said groups arranged in said predetermined pattern; meansmovably mounted for magnetically supporting a group of said leads in aninitial position to align said headed ends in a plane with said unheadedends depending downwardly into said groups of bores; a locking plateinterposed between said supporting means and said transfer member andhaving a plurality of groups of keyhole-shaped openings formed thereinand arranged in said predetermined pattern, with a circular portion ofeach of said openings aligned initially with one of the bores in saidtransfer member for receiving said groups of leads, said keyhole openinghaving a slotted portion which is narrower than the diameter of theheaded end and the washer; means mounting said locking plate for slidingmovement to position slotted portions of said keyhole openings over saidbores in said transfer member and to confine said washers and saidheaded ends between said locking plate and said supporting means; meansfor holding said plurality of groups of washers below the unheaded endsof said leads with each of said groups of washers arranged in saidpredetermined pattern and with each of said washers aligned with one ofsaid bores in said transfer member; a second locking plate, having aplurality of openings formed therein, said second locking plateinterposed between said holding means and said transfer member forguiding said wafers into engagement with a bottom surface of saidtransfer member when said fixture is inverted, each of said openings insaid plate having a slot extending radially therefrom, said slot beingnarrower than the diameter of a wafer; and means mounting said plate forsliding movement to lock said wafers against said transfer member and topermit one lead of each of said groups to be received in one slot beforesaid fixture is returned to the initial position.
 10. In a fixture forassembling a plurality of groups of paramagnetic leads, each of saidleads having headed and unheaded ends, with a plurality of groups ofwashers, and then with a plurality of wafers, each having apredetermined pattern of apertures, said leads held initially inparallel, spaced relation with said headed ends oriented upwardly: atransfer member having a plurality of groups of bores formedtherethrough, each of said groups having said bores arranged in saidpredetermined pattern; magnetic means for supporting said leads withsaid headed ends aligned in a plane and with said unheaded ends receivedin said bores in said transfer member; a first locking plate interposedbetween said magnetic means and said transfer member and having aplurality of groups of keyhole-shaped openings formed therein andarrayed in said predetermined pattern with a circular portion of saidopenings aligned with the bores in said transfer member, and withslotted portions of said openings being narrower than said washers andsaid unheaded ends; means mounting said first locking plate for slidingmovement to position the slotted portions of said keyhole openings oversaid bores in said transfer member and to confine said washers and saidheaded ends between said locking plate and said magnetic means; meansfor holding said plurality of groups of wafers arranged in saidpredetermined patterns below the unheaded ends of said leads with eachof said washers aligned with one of said leads; a second locking platehaving a plurality of openings and interposed between said wafers andsaid transfer member for passing said wafers to slide along the unheadedends of said leads and against the bottom surface of said transfermember when said fixture is inverted, each of said openings alignedinitially with one of said groups of bores in said transfer member andhaving a slot formed therein radially extending therefrom, each of saidslots being narrower than the wafer and larger than the diameter of theunheaded end of the lead; a retaining plate slideably mounted betweensaid magnetic means and said first locking plate for engaging andholding the leads in the transfer member when said fixture is inverted;and means for slideably mounting said second locking plate to shift saidsecond locking plate to lock said wafers against said transfer memberand to permit one lead of each of said groups of leads to be received inone slot before said fixture is returned to said initial position.